1. Field of the Invention
The present invention relates to an image forming apparatus and method that forms an image on a recording medium.
2. Related Background Art
Up to now, there have been known image forming apparatuses in which, when plural conveyor portions such as rollers are used to convey a recording medium, the plural conveyor portions are controlled so as to form a certain amount of flexure (loop) in the recording medium due to the plural conveyor portions.
As an example of the image forming apparatuses, there has been known an image forming apparatus of an electrophotographic system which includes a transferring portion that transfers a toner image on a photosensitive drum onto the recording medium, and a fixing portion that fixes the toner image on the recording medium, which has been sent from the transferring portion, by, for example, a heat roller method.
To explain with reference to the above-mentioned image forming apparatus of the electrophotographic system, the following problem can be observed. That is, if a fixing roller or the like constituting the fixing portion varies in roller diameter due to heat, a conveying speed imported to the recording medium by the transferring portion and a conveying speed imported to the recording medium by the fixing portion become different from each other. In this case, the recording medium is pulled at both the transferring portion and the fixing portion, or a loop larger than necessary occurs to the recording medium, which may lead to deterioration in image quality.
In order to solve the above-mentioned problem, a method has been adopted in which a detection portion is provided to detect an amount of loop that is formed in the recording medium by the transferring portion and the fixing portion, and the plural conveyor portions such as the rollers are controlled to maintain the amount of loop formed in the recording medium by the transferring portion and the fixing portion at a given level.
However, in the conventional image forming apparatus, the recording medium is passed through the transferring portion while maintaining a given amount of loop formed in the recording medium, so that there arises another problem as follows. That is, when a trailing end of the recording medium passes through the transferring portion, the loop formed by the plural conveyor portions such as the rollers is released. As a result, the trailing end of the recording medium vibrates, and the unfixed toner image that has been transferred onto the paper is disturbed, which leads to the deterioration in image quality.